そのうちの「神君家康公御遺文」（慶長十九年二月二十五日付）に、「秀忠公御嫡男　竹千代君　御腹　春日局　三世将軍家光公也、左大臣」と記されていることを根拠としている。

YAKIRI's theory is based on an article within the book entitled, "Posthumous Writings of Ieyasu" (from March 25, 1614), where it is written that "Hidetada's eldest son was Takechiyo, born from Kasaga no Tsubone, and was the 3rd Shogun Iemitsu, Minister of the Left." - Wikipedia日英京都関連文書対訳コーパス

特に身分の高い武家や公家の姫君の側近くに仕える、五、六歳から十二歳ぐらいの「お小姓」（大名などに仕える武家の少年使用人である小姓とは別）と呼ばれる少女によく結われた髪型。

This hairstyle was worn by the girls called 'Okosho' (it is different from child servants of samurai family called "Kosho," who paged to daimyo [Japanese feudal lord] and so on), who was aged between five or six and 12 years old and attended on a daughter of a high-ranking samurai or a court noble. - Wikipedia日英京都関連文書対訳コーパス